The invention relates generally to a system for forming x-rays, and more particularly to a system configured to direct electron beams at a plurality of discrete spots on a target to form x-rays.
X-ray scanning has been used in medical diagnostics, industrial imaging, and security related applications. Commercially available x-ray sources typically utilize conventional thermionic emitters, which are helical coils made of tungsten wire and operated at high temperatures. Each thermionic emitter is configured to emit a beam of electrons to a single focal spot on a target. To obtain a total current of 10 to 20 mA with an electron beam size of 10 mm2, helical coils formed of a metallic wire having a work function of 4.5 eV must be heated to about 2600 K. Due to its robust nature, tungsten wire has been the electron emitter of choice.
There are disadvantages to the use of conventional thermionic filament emitters. Such filament emitters lack a uniform emission profile necessary for proper beam steering and focusing. Further, a higher electron beam current will cause a reduction in the lifetime of such filament emitters. Additionally, such filament emitters require high quiescent power consumption, which leads to the need for larger, more complex cooling architectures, a larger system envelope, and greater cost.